Gas filling system

ABSTRACT

Provided is a gas filling system capable of further improving SOC of a gas tank. A gas filling system includes a gas tank and a gas station. The gas station includes a gas feed line, a gas return line, a gas circulation pump configured to circulate the gas between the gas tank and the gas station through the gas feed line and the gas return line, and a precooler configured to cool the gas fed from the gas station to the gas tank through the gas feed line. The gas is supplied from the gas station to the gas tank while the gas cooled by the gas precooler to a temperature lower than a heat resistant temperature of the gas tank is being circulated between the gas tank and the gas station.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese patent application No. 2016-155012, filed on Aug. 5, 2016, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

The present invention relates to a gas filling system.

A gas filling system in which a high pressure gas is supplied from a gas station to a gas tank mounted on a vehicle or the like to fill the gas tank with the gas is well known. Japanese Unexamined Patent Application Publication No. 2011-033068 discloses a gas filling system that cools a hydrogen gas that is at about room temperature supplied from an accumulator for storing a pressurized hydrogen gas to a predetermined temperature by heat exchange in a precooler, and then fills a gas tank with the cooled gas. The amount of the gas to be supplied to the gas tank is increased by cooling the gas before supplying it to the gas tank.

SUMMARY

Supplying of a hydrogen gas to a fuel cell vehicle is commonly carried out by a method complying with the filling protocol standard (SAE J2601). While gas is being supplied to a gas tank, a gas temperature in the gas tank gradually rises due to heat generated by adiabatic compression of the gas in the gas tank. According to the above filling protocol, the upper limit of the gas temperature in the gas tank is defined as 85° C. The upper limit value (85° C.) of the gas temperature in the gas tank defined by the filling protocol is specified as the heat resistant temperature in the gas tank (heat resistant temperature of the gas tank in the standard). While the gas is being supplied, the temperature of the gas in the gas tank rises by adiabatic compression of the gas. For this reason, it is necessary to prevent the temperature of the gas in the gas tank from exceeding the heat resistant temperature of the gas tank while the gas is being supplied to the gas tank.

An amount of a hydrogen gas that can be supplied to the gas tank, i.e., hydrogen gas density ρ in the gas tank, is calculated by the formula ρ=M/V=MP/(nRT) based on the equation of state for gas (PV=nRT), where P[Pa] represents the pressure of the hydrogen gas, T[K] represents the temperature of the hydrogen gas, and M[kg] represents mass of the hydrogen gas. Further, R is a gas constant, and n is the number of moles of the hydrogen gas. The hydrogen gas density ρ in the gas tank is proportional to the pressure P in the gas tank and inversely proportional to the temperature T in the gas tank. That is, in order to increase the hydrogen gas density ρ in the gas tank, it is necessary to increase the pressure of the hydrogen gas to be supplied or to lower the temperature of the hydrogen gas to be supplied.

As described above, the gas filling system described in Japanese Unexamined Patent Application Publication No. 2011-033068 increases the hydrogen gas density ρ in the gas tank by exchanging heat using the precooler to thereby lower the temperature of the hydrogen gas to be supplied. However, in the gas filling system described in Japanese Unexamined Patent Application Publication No. 2011-033068, in order to further lower the temperature of the hydrogen gas to be supplied for further increasing the hydrogen gas density ρ in the gas tank, it is necessary to further improve the cooling capacity of the precooler. That is, it is necessary to replace the precooler by one with a higher refrigerating ability which will cost more than the replaced one. In addition, if the cooling capacity of the precooler is improved, it is necessary to replace the members of the gas station, such as a seal member, by those that can withstand a lower temperature, which will cost more, in each element of the gas station accordingly. Consequently, the installation cost of the gas station will be greatly increased.

On the other hand, the pressure of the hydrogen gas to be supplied could be increased while maintaining the cooling capacity of the precooler. However, in this way, the temperature of the gas in the gas tank will exceed the heat resistant temperature of the gas tank while the gas is being supplied to the gas tank. Hereinafter, a mechanism in which an increase in the pressure of the hydrogen gas to be supplied while maintaining the cooling capacity of the precooler causes the temperature of the gas in the gas tank to exceed the heat resistant temperature of the gas tank will be described with reference to FIG. 8.

FIG. 8 is a graph showing a relationship between the pressure in the hydrogen gas and the temperature in the gas tank when the gas is being supplied to the gas tank by a gas filling system developed by the inventors. The hydrogen gas cooled to −40° C. by the precooler is supplied to the gas tank from the gas station. In the graph, a horizontal axis represents the temperature (unit: ° C.) of the hydrogen gas in the gas tank, and a vertical axis represents the pressure of the hydrogen gas in the gas tank (unit: MPa). A solid line Ed1 represents an isopycnic line with SOC of 100%, and a solid line Ed4 represents an isopycnic line with the SOC of 130%. The SOC (State Of Charge) is the filling rate of the gas tank, the hydrogen gas density when the temperature is 15° C. and the pressure is at a Normal Working Pressure (NWP) of the gas tank is 100%.

As shown in FIG. 8, when the gas is being supplied to the gas tank from the empty state (state A3) to the SOC of 100%, the pressure of the hydrogen gas and the temperature of the hydrogen gas in the gas tank transition from the state A3 to the state B3 as indicated by the broken line L21. In the state at the completion of filling (state B3), the pressure of the hydrogen gas in the gas tank is 87.5 MPa. At this time, the temperature of the hydrogen gas in the gas tank is 85° C., which is the heat resistant temperature of the gas tank.

On the other hand, when the gas is being supplied to the gas tank from the empty state (state A3) to the SOC of 130%, the pressure of the hydrogen gas and the temperature of the hydrogen gas in the gas tank transition from the state A3 to the state C3 as indicated by the broken line L22. In the state at the completion of filling (state C3), the pressure of the hydrogen gas in the gas tank exceeds 130 MPa which is higher than 87.5 MPa of the state B3. Therefore, in the state C3, the gas in the gas tank is more adiabatically compressed than in the state B3. Accordingly, in the state C3, the temperature of the hydrogen gas in the gas tank exceeds 100° C., which is higher than the heat resistant temperature (85° C.) of the gas tank. That is, when the gas is being supplied to the gas tank up to the SOC of 130%, if the cooling capacity of the precooler is the same as that when the gas tank is filled up to the SOC of 100%, the temperature of the hydrogen gas in the gas tank at the completion of filling exceeds 85° C., which is the heat resistant temperature of the gas tank.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gas filling system capable of further improving SOC of a gas tank while preventing a temperature of a gas in the gas tank from exceeding a heat resistant temperature of the gas tank without a significant increase in cost.

In an aspect of the present invention, a gas filling system includes a gas tank and a gas station configured to supply a gas to the gas tank. The gas station includes: a gas feed line configured to feed the gas from the gas station to the gas tank; a gas return line configured to return the gas in the gas tank to the gas station; a gas circulation pump configured to circulate the gas between the gas tank and the gas station through the gas feed line and the gas return line; and a gas cooling unit configured to cool the gas fed from the gas station to the gas tank through the gas feed line. The gas is supplied from the gas station to the gas tank while the gas cooled by the gas cooling unit to a temperature lower than a heat resistant temperature of the gas tank is being circulated between the gas tank and the gas station. When the gas tank is filled with the gas, the gas is supplied from the gas station to the gas tank while the gas cooled by the gas cooling unit to the temperature lower than the heat resistant temperature of the gas tank is being circulated between the gas tank and the gas station by the gas circulation pump. In this way, the gas in the gas tank is cooled to the temperature lower than the heat resistant temperature of the gas tank. Thus, the temperature of the gas in the gas tank 3 will not exceed the heat resistant temperature of the gas tank while the gas is being supplied to the gas tank. Further, when the gas is being supplied while being circulated, the gas returned from the gas tank to the gas station is cooled by the gas cooling unit, whereby the pressure is reduced. Thus the gas can be replenished from the gas station to the gas tank by an amount of the reduction in the pressure of the gas by the cooling. Accordingly, it is possible to further increase SOC of the gas tank compared with the case where the gas is not circulated while the gas is being supplied to the gas tank.

Further, in the gas filling system, after a temperature of the gas in the gas tank has risen to a predetermined temperature, the gas is supplied from the gas station to the gas tank while the gas is being circulated by the gas cooling unit between the gas tank and the gas station. If the gas is circulated between the gas tank and the gas station from the beginning when the gas is being supplied to the gas tank, it takes more time to fill the gas tank with the gas as compared with the case where there is no gas circulation. Therefore, the time required to fill the gas tank with the gas can be shortened by filling the gas tank with the gas without the gas circulation until the temperature of the gas in the gas tank reaches a predetermined temperature (e.g., withstand temperature of the gas tank). Accordingly, it is possible to further increase SOC of the gas tank without preventing the time required to fill the gas tank with the gas from being increased by supplying the gas from the gas station to the gas tank while the gas is being circulated by the gas cooling unit between the gas tank and the gas station after the gas temperature in the gas tank has reached the predetermined temperature.

Furthermore, in the gas filling system, the gas tank is mounted on a vehicle, and the vehicle includes a gas feeding connection port for connecting the gas tank to the gas feed line and a gas returning connection port for connecting the gas tank to the gas return line, and shapes of connection parts of the gas feeding connection ports and the gas returning connection port differ from each other. Thus, it is possible to prevent the gas feed line from being incorrectly connected to the gas returning connection port and to prevent the gas return line from being incorrectly connected to the gas feeding connection port.

According to the present invention, it is possible to further increase SOC of a gas tank while preventing a temperature of a gas in a gas tank from exceeding a heat resistant temperature of the gas tank without a significant increase in cost.

The above and other objects, features and advantages of the present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing showing a schematic configuration of a gas filling system according to embodiments;

FIG. 2 is a drawing showing a specific configuration of the gas filling system according to the embodiments;

FIG. 3 is a drawing for describing a gas filling method of the gas filling system according to the embodiments;

FIG. 4 is a drawing for describing a transition of a pressure in a gas tank and a temperature in the gas tank when a hydrogen gas is being circulated between the gas tank and a gas station from SOC of 100%;

FIG. 5 is a table summarizing the pressures and the temperatures in the gas tank when the gas tank is filled and used for respective SOCs;

FIG. 6 is a drawing for describing a gas filling method by a gas filling system according to a second embodiment;

FIG. 7 is a table summarizing comparisons between the pressures and temperatures in the gas tank when the gas tank is filled so that the SOC becomes 100% by the gas filling method performed by the gas filling system according to the second embodiment and when the gas tank is filled so that the SOC becomes 100% by a gas filling method where there is no gas circulation; and

FIG. 8 is a graph showing a relationship between the pressure and the temperature of the hydrogen gas in the gas tank when the gas is being supplied to the gas tank by a gas filling system developed by the inventors.

DESCRIPTION OF EMBODIMENTS First Embodiment

Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. As an example of a gas filling system, an example of supplying a hydrogen gas to a fuel cell vehicle equipped with a fuel cell system from a gas station will be described. As is well known, the fuel cell system includes a fuel cell or the like that generates power by an electrochemical reaction of a fuel gas (e.g., hydrogen gas) and an oxidization gas (e.g., air).

First, a schematic configuration of the gas filling system 1 according to this embodiment will be described with reference to FIG. 1. FIG. 1 is a drawing showing a schematic configuration of a gas filling system 1 according to this embodiment. As shown in FIG. 1, the gas filling system 1 according to the this embodiment includes a gas tank 3 and a gas station 2 that supplies a gas to the gas tank 3. The gas station 2 includes a gas feed line 11, a gas return line 12, a gas circulation pump 14 for circulating a gas between the gas tank 3 and the gas station 2 through the gas feed line 11 and the gas return line 12, and a precooler 18 as a gas cooling unit for cooling the gas fed from the gas station 2 to the gas tank 3 through the gas feed line 11. In the gas filling system 1, the gas is supplied from the gas station 2 to the gas tank 3 while the gas cooled by the precooler 18 to a temperature lower than the heat resistant temperature of the gas tank 3 is being circulated between the gas tank 3 and the gas station 2.

When the gas tank 3 is filled with the gas, the gas is supplied from the gas station 2 to the gas tank 3 while the gas cooled by the precooler 18 to a temperature lower than the heat resistant temperature of the gas tank 3 is being circulated between the gas tank 3 and the gas station 2 by the gas circulation pump 14. By doing so, the gas in the gas tank 3 is cooled to the temperature lower than the heat resistant temperature of the gas tank 3. In this way, the temperature of the gas in the gas tank 3 will not exceed the heat resistant temperature of the gas tank 3 while the gas is being supplied to the gas tank 3. Further, when the gas is being supplied to the gas tank 3 while being circulated, the gas returned from the gas tank 3 to the gas station 2 is cooled by the precooler 18, whereby the pressure is reduced. Thus the gas can be replenished from the gas station 2 to the gas tank 3 by an amount of the reduction in the pressure of the gas by the cooling. Accordingly, it is possible to further increase the SOC of the gas tank 3 compared with the case where the gas is not circulated while the gas is being supplied to the gas tank 3.

Next, a more specific configuration of the gas filling system 1 according to this embodiment will be described with reference to FIG. 2. FIG. 2 is a drawing showing a specific configuration of the gas filling system 1.

As shown in FIG. 2, the gas filling system 1 includes the gas tank 3 and the gas station 2.

The gas tank 3 is mounted on a vehicle 50. The gas tank 3 is a fuel gas supply source for a fuel cell and is a high pressure tank capable of storing a hydrogen gas. The hydrogen gas in the gas tank 3 is supplied to the fuel cell through a supply pipeline (not shown). In the gas tank 3, a pressure sensor 51 for detecting the pressure in the gas tank 3 and a temperature sensor 52 for detecting the temperature inside the gas tank 3 are provided.

The gas station 2 includes the gas feed line 11, the gas return line 12, the gas circulation pump 14, accumulators 15, and the precooler (gas cooling unit) 18. The gas feed line 11 is a gas flow path for feeding a gas from the gas station 2 to the gas tank 3 and is indicated by the dashed line in FIG. 2. The gas return line 12 is a gas flow path for returning the gas in the gas tank 3 to the gas station 2 and is indicated by the broken line in FIG. 2.

The gas circulation pump 14 circulates the gas between the gas tank 3 and the gas station 2 through the gas feed line 11 and the gas return line 12. As the gas circulation pump 14, for example, a blower fan can be used. The accumulators 15 are for storing a hydrogen gas which has been pressurized to a predetermined pressure (e.g., 95 MPa), and is provided in the gas feed line 11. A flow rate control valve 48 for adjusting the flow rate of the hydrogen gas supplied to the gas feed line 11 is provided in the accumulators 15. Note that the accumulators 15 may include a plurality of accumulator tanks each having different pressures to be accumulated.

The precooler 18 cools the gas fed from the gas station 2 to the gas tank 3 through the gas feed line 11 to a temperature lower than the heat resistant temperature of the gas tank 3 by heat exchange. Any one of a partition wall type, an intermediate medium type, and a storage type can be used as a form of the heat exchange by the precooler 18, and a known structure can be employed as a structure of the precooler 18. In the example shown in FIG. 2, the form of the heat exchange by the precooler 18 is the intermediate medium type where a refrigerant is circulated between a precooling heat exchanger 32 and a refrigerator 31, and heat is exchanged between the hydrogen gas and the refrigerant in the precooling heat exchanger 32.

The gas station 2 further includes a dispenser (filler) 40 for the user to perform the filling operation when filling the gas tank 3 with gas. The gas station 2 further includes a control unit 20 for controlling the filling of the gas tank 3 with the gas from the gas station 2.

The dispenser 40 has a flow rate control valve 44 for adjusting the flow rate of the hydrogen gas supplied from the gas station 2 to the gas tank 3 and a flow meter 43 for measuring a flow rate of the hydrogen gas supplied from the gas station 2 to the gas tank 3. In the gas station 2, parts other than the dispenser 40 are defined as a gas station main body 30. The flow rate control valve 44 is an electrically driven valve and includes, for example, a step motor as a drive source. The flow rate control valve 44 adjusts the flow rate of the hydrogen gas by changing the degree of valve opening by the step motor in accordance with a command from the control unit 20. Then the flow rate of the hydrogen gas supplied to the gas tank 3 is controlled. The controlled flow rate of the hydrogen gas to be supplied is measured by the flow meter 43, and the control unit 20 performs feedback control on the flow rate control valve 44, so that in response to a result of the measurement, a desirable flow rate will be achieved.

The control unit 20 is configured as a microcomputer including a CPU, a ROM, and a RAM. The CPU executes a desired calculation according to a control program and performs various processes and control. The ROM stores the control program and control data to be processed by the CPU, and the RAM is mainly used as various work areas for control processing. Although the control unit 20 is provided in the dispenser 40 in FIG. 2, it is not limited to this, and instead the control unit 20 may be provided in the gas station main body 30. Alternatively, the control unit 20 may be provided in the vehicle 50 instead of the gas station 2.

The above-described precooling heat exchanger 32 of the precooler 18 is preferably installed in the dispenser 40 in order for the hydrogen gas to be cooled at a position just before it is supplied to the gas tank 3. A main stop valve 47 for switching supplying and stopping of the hydrogen gas from the gas station 2 to the gas tank 3 is provided in the gas feed line 11 at a position downstream of the precooler 18 in the gas flow direction. A pressure sensor 41 for detecting the pressure of the hydrogen gas supplied to the gas tank 3 and a temperature sensor 42 for detecting the temperature of the hydrogen gas supplied to the gas tank 3 are provided in the gas feed line 11 at positions downstream of the precooler 18 in the gas flow direction

A part of the gas feed line 11 is extended from the dispenser 40 as a gas feed hose. A part of the gas return line 12 is extended from the dispenser 40 as a gas return hose. A gas feeding nozzle 45 is provided at a leading end of the gas feed hose and a gas returning nozzle 46 is provided at a leading end of the gas return hose.

In the vehicle 50, a gas feeding receptacle (gas feeding connection port) 53 and a gas returning receptacle (gas returning connection port) 54 for connecting the gas tank 3 to the gas feed line 11 are provided. That is, the gas feeding receptacle 53 is coupled to the gas feeding nozzle 45, and the gas returning receptacle 54 is coupled to the gas returning nozzle 46. In order to simplify the connecting operation, the gas feeding receptacle 53 and the gas returning receptacle 54 are preferably provided in the same fuel lid in the vehicle 50. In order to prevent the gas feeding nozzle 45 from being incorrectly coupled to the gas returning receptacle 54 and to prevent the gas returning nozzle 46 from being incorrectly coupled to the gas feeding receptacle 53, the shapes of the connection parts of the gas feeding receptacle 53 and the gas returning receptacle 54 are preferably different from each other.

A check valve 56 for preventing backflow of the hydrogen gas is provided in a filling pipeline 55 that connects the gas feeding receptacle 53 to the gas tank 3. A main stop valve 58 and a pressure reducing valve 59 for stopping the gas from being discharged are provided in a recirculation pipeline 57 that connects the gas tank 3 to the gas returning receptacle 54. When the pressure of the gas to be discharged from the gas tank 3 to the gas return line 12 is higher than a predetermined pressure (e.g., 87.5 MPa), the pressure reducing valve 59 reduces the pressure of the gas to the predetermined pressure.

Next, a gas filling method of the gas filling system 1 according to this embodiment will be described with reference to FIG. 3. In the following description, reference will also be made to FIG. 2 as appropriate. FIG. 3 is a drawing for describing the gas filling method of the gas filling system 1. In FIG. 3, a horizontal axis of the graph represents the temperature (unit: ° C.) of the hydrogen gas in the gas tank 3, and a vertical axis of the graph represents the pressure (unit: MPa) of the hydrogen gas in the gas tank 3. A solid line Ed1 is an isopycnic line with the SOC of 100%, a solid line Ed2 is an isopycnic line with the SOC of 120%, a solid line Ed3 is an isopycnic line with the SOC of 125%, and a solid line Ed4 is an isopycnic line with the SOC of 130%.

As shown in FIG. 3, firstly, from the empty state of the gas tank 3 (state A1) to the state with the SOC of 100% (state B1), the hydrogen gas is supplied to the gas tank 3 without circulating the hydrogen gas between the gas tank 3 and the gas station 2. That is, the main stop valve 47 of the gas feed line 11 is opened, and the high pressure hydrogen gas cooled by the precooler 18 to a temperature of −40° C. is supplied from the gas station 2 to the gas tank 3. At this time, the main stop valve 58 of the recirculation pipeline 57 is kept closed so that the hydrogen gas in the gas tank 3 will not be returned to the gas station 2. Thus, the pressure of the hydrogen gas and the temperature of the hydrogen gas in the gas tank 3 transition as indicated by the broken line L1. That is, the gas temperature in the gas tank 3 rises from an external temperature (15° C. in this example) to 85° C., which is the heat resistant temperature of the gas tank 3, by the above-described adiabatic compression of the gas, and the gas pressure in the gas tank rises from 0 MPa to a predetermined pressure (87.5 MPa in this example).

Next, the hydrogen gas is supplied from the gas station 2 to the gas tank 3 while the hydrogen gas cooled by the precooler 18 is being circulated between the gas tank 3 and the gas station 2. That is, after the temperature of the hydrogen gas in the gas tank 3 detected by the temperature sensor 52 has risen to the heat resistant temperature of the gas tank 3, the control unit 20 opens the main stop valve 58 of the recirculation pipeline 57, and the hydrogen gas is circulated by the gas circulation pump 14 between the gas tank 3 and the gas station 2. The hydrogen gas circulating between the gas tank 3 and the gas station 2 is cooled by the precooler 18. The hydrogen gas returned from the gas tank 3 to the gas station 2 is cooled by the precooler 18 to a temperature less than 85° C., which is the heat resistant temperature of the gas tank 3, whereby the pressure is reduced. Therefore, the control unit 20 controls the flow rate control valve 48 to replenish the hydrogen gas from the accumulators 15 so that the pressure of the hydrogen gas in the gas tank 3 detected by the pressure sensor 51 is maintained at a predetermined pressure (87.5 MPa in this example). That is, in the gas tank 3, the amount of the hydrogen gas is increased by the amount of the hydrogen gas replenished by the accumulators 15.

In order to increase the SOC of the gas tank 3 from 100% to 120%, it is necessary to continue the circulation of the hydrogen gas from the state B1 to the state C1 where the broken line L2 crosses the isopycnic line Ed2 with the SOC of 120%, that is, until the temperature of the hydrogen gas in the gas tank 3 is reduced from 85° C. to about 0° C. In this case, the hydrogen gas supplied from the gas station 2 to the gas tank 3 needs to be cooled to a temperature of 0° C. by the precooler 18.

In order to increase the SOC of the gas tank 3 from 100% to 125%, it is necessary to continue the circulation of the hydrogen gas from the state B1 to the state D1 where a solid line L2 crosses the isopycnic line Ed3 with the SOC of 125%, that is, until the temperature of the hydrogen gas in the gas tank 3 is reduced from 85° C. to −20° C. In this case, the hydrogen gas supplied from the gas station 2 to the gas tank 3 needs to be cooled by the precooler 18 to the temperature of −20° C.

In order to increase the SOC of the gas tank 3 from 100% to 130%, it is necessary to continue the circulation of the hydrogen gas from the state B1 to the state E1 where the solid line L2 crosses the isopycnic line Ed4 with the SOC of 130%, that is, until the temperature of the hydrogen gas in the gas tank 3 is reduced from 85° C. to −35° C. In this case, the hydrogen gas supplied from the gas station 2 to the gas tank 3 needs to be cooled by the precooler 18 to a temperature of −35° C.

FIG. 4 is a drawing for describing a transition of the pressure in the gas tank and the temperature in the gas tank when the hydrogen gas is circulated between the gas tank 3 and the gas station 2 from the state where the SOC is 100%. In FIG. 4, a horizontal axis of the graph represents time (unit: seconds). Further, a broken line represents the SOC of the gas tank 3 (unit of the vertical axis is %), a dashed-dotted line represents the pressure of the hydrogen gas in the gas tank 3 (unit of the vertical axis is MPa), a solid line represents a circulation flow rate of the hydrogen gas (unit of the vertical axis is g/sec), and an alternate long and two short dashes line represents the temperature of the hydrogen gas in the gas tank 3 (unit of the vertical axis is ° C.).

As shown in FIG. 4, the flow rate of the hydrogen gas circulating between the gas tank 3 and the gas station 2 is maintained at a constant value (60 g/sec). As described above, by replenishing the hydrogen gas from the accumulators 15, the pressure of the hydrogen gas in the gas tank 3 is maintained at the predetermined pressure of 87.5 MPa. A temperature Ttank of the hydrogen gas in the gas tank 3 is gradually reduced from 85° C., which is the heat resistant temperature of the gas tank 3. As described with reference to FIG. 3, when the temperature Ttank of the hydrogen gas in the gas tank 3 reaches about 0° C., the SOC of the gas tank 3 becomes 120%, when the temperature Ttank of the hydrogen gas in the gas tank 3 reaches about −20° C., the SOC of the gas tank 3 becomes 125%, and when the temperature Ttank of the hydrogen gas in the gas tank 3 reaches about −35° C., the SOC of the gas tank 3 becomes 130%.

Accordingly, as shown in FIG. 4, the time taken for the circulation of the gas while cooling the gas is about 100 seconds for the SOC of 120%, about 150 seconds for the SOC of 125% and about 270 seconds for the SOC of 130%. Since the time required to fill the gas tank 3 with the hydrogen gas up to the SOC of 100% without the gas circulation is about 180 seconds, the time required to achieve up to the SOC of 120% is about 280 seconds (100 seconds+180 seconds), the time required to achieve up to the SOC of 125% is about 330 seconds (150 seconds+180 seconds), and the time required to achieve up to the SOC of 130% is 450 seconds (270 seconds+180 seconds).

FIG. 5 is a table summarizing the pressures and the temperatures in the gas tank when the gas is being supplied to the gas and the fuel cell system is in-operation for respective SOCs. As shown in FIG. 5, with different SOCs for the gas tank, the maximum pressure of the gas in the gas tank 3 varies as a matter of course when the fuel cell system is in-operation (assumed the fuel cell system is in-operation at an external temperature of 50° C.). However, in the gas filling system 1 according to this embodiment, the maximum pressure of the gas in the gas tank 3 while the gas is being supplied to the gas tank 3 is 87.5 MPa, which is the predetermined pressure, for any of the SOCs 100%, 120%, 125%, and 130%. Moreover, the maximum temperature of the gas in the gas tank 3 while the gas is being supplied to the gas tank 3 is 85° C., which is the heat resistant temperature of the gas tank 3, for any of SOCs 100%, 120%, 125%, and 130%.

The cooling temperature of the hydrogen gas supplied from the gas station 2 to the gas tank 3 when the gas tank 3 is filled from the empty state to the state with the SOC of 100% is −40° C. for any of the SOCs 100%, 120%, 125%, and 130%. At this time, the cooling capacity of the precooler 18 is −40° C. On the other hand, when the hydrogen gas is circulated between the gas tank 3 and the gas station 2, it is necessary to set the cooling temperature of the hydrogen gas supplied from the gas station 2 to the gas tank 3 to −35° C. for the SOC of 130%, −20° C. for the SOC of 125%, and 0° C. for the SOC of 120%. In any case, it is higher than −40° C., which is the cooling capacity of the precooler 18. Therefore, the SOC of the gas tank 3 can be increased from 100% to 120%, to 125%, and to 130% without changing the cooling capacity of the precooler 18. In addition, the time required to fill the gas tank is within 10 minutes for any of the SOCs 100%, 120%, 125%, and 130%. Thus, the gas filling system of this embodiment has a sufficient competitive advantage compared with rapid charging of electric vehicles which take about 20 to 30 minutes.

As described above, when the gas tank 3 is filled with the gas, the gas is supplied from the gas station 2 to the gas tank 3 while the gas cooled by the precooler 18 to the temperature lower than the heat resistant temperature of the gas tank 3 is being circulated between the gas tank 3 and the gas station 2 by the gas circulation pump 14. By doing so, the gas in the gas tank 3 is cooled to the temperature lower than the heat resistant temperature of the gas tank 3. In this way, the temperature of the gas in the gas tank 3 will not exceed the heat resistant temperature of the gas tank 3 while the gas is being supplied to the gas tank 3. Further, when the gas is being supplied while being circulated, the gas returned from the gas tank 3 to the gas station 2 is cooled by the precooler 18, whereby the pressure is reduced. Thus the gas can be replenished from the gas station 2 to the gas tank 3 by an amount of the reduction in the pressure of the gas by the cooling. Accordingly, it is possible to further increase the SOC of the gas tank 3 compared with the case where the gas is not circulated while the gas is being supplied to the gas tank 3.

Second Embodiment

Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. A configuration of a gas filling system according to this embodiment is the same as that described with reference to FIG. 2 in the first embodiment. This embodiment differs from the first embodiment in the pressure of the hydrogen gas in the gas tank 3 just before circulating the gas between the gas tank 3 and the gas station 2.

A gas filling method of the gas filling system according to this embodiment will be described. In the following description, reference will also be made to FIG. 2 as appropriate. FIG. 6 is a drawing for describing the gas filling method of the gas filling system according to this embodiment. In this example, a horizontal axis of the graph represents the temperature of the gas (unit: ° C.), and a vertical axis of the graph represents the pressure of the gas (unit: MPa). A solid line Ed1 is an isopycnic line with the SOC of 100%. When the gas is supplied as indicated by a dashed line L1 in FIG. 3, the cooling temperature of the hydrogen gas supplied from the gas station 2 to the gas tank 3 is −40° C. On the other hand, when the gas is supplied as indicated by a broken line L11 in FIG. 6, the cooling temperature of the hydrogen gas supplied from the gas station 2 to the gas tank 3 is −25° C.

As shown in FIG. 6, firstly, the hydrogen gas is only supplied from the gas station 2 to the gas tank 3 through the gas feed line 11, and the gas is not returned from the gas tank 3 to the gas station 2 from the empty state of the gas tank 3 (state A2) until the state where the pressure in the gas tank 3 is 60 MPa (state B2). That is, the main stop valve 47 of the gas feed line 11 is opened to supply the hydrogen gas from the gas station 2 to the gas tank 3. However, the main stop valve 58 of the recirculation pipeline 57 is kept closed to stop the hydrogen gas in the gas tank 3 from returning to the gas station 2. Thus, the pressure of the hydrogen gas and the temperature of the hydrogen gas in the gas tank 3 transition as indicated by the broken line L11. That is, the gas pressure in the gas tank 3 rises from 0 MPa to 60 MPa, and the gas temperature in the gas tank 3 rises from an external temperature (15° C. in this example) to 85° C., which is the heat resistant temperature of the gas tank 3, by the above-described adiabatic compression of the gas. The pressure (60 MPa) in the gas tank 3 in the state B2 is lower than the pressure (87.5 MPa) in the state B1 when the gas tank 3 is filled up to the SOC of 100%, which is indicated by the broken line L1 in FIG. 3, where there is no gas circulation.

Next, the hydrogen gas is supplied from the gas station 2 to the gas tank 3 while the hydrogen gas cooled by the precooler 18 is being circulated between the gas tank 3 and the gas station 2. That is, after the temperature of the hydrogen gas in the gas tank 3 detected by the temperature sensor 52 has risen to the heat resistant temperature of the gas tank 3, the control unit 20 opens the main stop valve 58 of the recirculation pipeline 57, and the gas circulation pump 14 circulates the hydrogen gas between the gas tank 3 and the gas station 2. The hydrogen gas circulating between the gas tank 3 and the gas station 2 is cooled by the precooler 18. The hydrogen gas returned from the gas tank 3 to the gas station 2 is cooled by the precooler 18 to a temperature of 85° C. or lower, which is the heat resistant temperature of the gas tank 3, whereby the pressure is reduced. Therefore, the control unit 20 controls the flow rate control valve 48 to replenish the hydrogen gas from the accumulators 15 so that the pressure of the hydrogen gas in the gas tank 3 detected by the pressure sensor 51 is maintained at a predetermined pressure (60 MPa in this example). That is, in the gas tank 3, the amount of the hydrogen gas is increased by the amount of the hydrogen gas replenished by the accumulators 15. If the circulation of the hydrogen gas is continued until the solid line L12 crosses the isopycnic line Ed1 of the SOC of 100%, that is, until the hydrogen gas temperature in the gas tank 3 reaches −25° C., the SOC of the gas tank 3 will become 100%. Therefore, while the hydrogen gas is being circulated between the gas tank 3 and the gas station 2, it is necessary to set the cooling temperature of the hydrogen gas supplied from the gas station 2 to the gas tank 3 to −25° C.

FIG. 7 is a table summarizing comparisons between the pressures and temperatures in the gas tank when the gas tank is filled so that the SOC becomes 100% by the gas filling method performed by the gas filling system according to this embodiment and when the gas tank is filled so that the SOC becomes 100% by a gas filling method according to a comparative example. The gas filling method according to the comparative example is a gas filling method where there is no gas circulation. When the gas tank is filled so that the SOC becomes 100% by the gas filling method according to the comparative example, the temperature and the pressure in the gas tank while the gas is being supplied to the gas tank 3 transition as indicated by the broken line L1 in FIG. 3.

As shown in FIG. 7, the maximum temperature of the gas in the gas tank 3 while the gas is being supplied to the gas tank 3 is 85° C. in either of the gas filling system according to this embodiment and the gas filling method according to the comparative example. On the other hand, the maximum pressure of the gas in the gas tank 3 while the gas is being supplied to the gas tank 3 is 87.5 MPa in the gas filling method according to the comparative example, while in the gas filling system according to this embodiment, it is 60 MPa, which is lower than 87.5 MPa. Accordingly, when the gas tank 3 is filled until the SOC becomes 100% by the gas filling system according to this embodiment, elements in the gas station 2 can be replaced by ones with lower withstand voltages as compared with the case when the gas tank 3 is filled until the SOC becomes 100% by the gas filling system according to the comparative example. Accordingly, the installation cost of the gas station can be further reduced.

When the gas tank is filled until the SOC becomes 100% by the gas filling method according to the comparative example, the cooling temperature of the hydrogen gas supplied from the gas station 2 to the gas tank 3 is −40° C. At this time, the cooling capacity of the precooler 18 is −40° C. On the other hand, when the gas tank is filled until the SOC becomes 100% by the gas filling system according to this embodiment, the cooling temperature of the hydrogen gas supplied from the gas station 2 to the gas tank 3 is −25° C. At this time, the cooling capacity of the precooler 18 is −25° C. That is, when the gas tank is filled until the SOC becomes 100% by the gas filling system according to this embodiment, the precooler 18 can be replaced by one with a lower cooling capacity as compared with the case when the gas tank 3 is filled until the SOC becomes 100% by the gas filling system according to the comparative example. Accordingly, the installation cost of the gas station can be further reduced.

Note that the present invention is not limited to the above embodiments, and changes can be made thereto as appropriate without departing from the scope of the invention. Although a compressor is used to pressurize the gas (having a pressure of, for example, 20 to 45 MPa) in a tank of a gas transport vehicle to a predetermined pressure (for example, 82 to 95 MPa) and supply the gas to accumulators of a gas station, this compressor may be used also as a gas circulation pump in a gas filling system. In the above embodiments, the heat resistant temperature of the gas tank is set to the upper limit value (85° C.) of the gas temperature in the gas tank specified by the filling protocol. However, the heat resistant temperature of the gas tank may be set to a temperature at which the function or physical property of the gas tank can be maintained without deterioration such as deformation alteration in a state where no force is applied.

The gas may be circulated between the gas tank and the gas station from the beginning when the gas tank is filled with the gas. However, if the gas is circulated between the gas tank and the gas station from the beginning when the gas tank is filled with the gas, it takes more time to fill the gas tank with the gas as compared with the case where there is no gas circulation. This is because, assuming that the gas flow rate is the same in the case where the gas is circulated and the case where the gas is not circulated, when the gas tank is filled with the gas in the case where the gas is circulated, since the gas supplied once in the gas tank flows out, it takes more time to fill the gas tank with the gas as compared with when the gas tank is filled in the case where there is no gas circulation. Therefore, as in the above embodiments, the time required to fill the gas tank with the gas can be shortened by filling the gas tank with the gas without circulating the gas until the temperature of the gas in the gas tank reaches a predetermined temperature (withstand temperature of the gas tank). For example, suppose that the temperature of the gas in the gas tank reaches the predetermined temperature (withstand temperature of the gas tank) at the SOC of 100% when the gas is supplied without being circulated. Supposing that a target number of the SOC is 130%, in order to increase the target SOC to 130% from the state where the SOC reaches 100% by circulating the gas, a difference between the current SOC and the target SOC, which should be reached by the gas circulation, is 30% (130%-100%). On the other hand, when the gas is circulated from the state where the SOC has not reached 100% to the target SOC of 130%, a difference between the current SOC and the target SOC, which should be reached by the gas circulation, is greater than 30%. That is, the difference between the current SOC and the target SOC is smaller when the SOC is increased from the state where the SOC reaches 100% to the target SOC 130% by circulating the gas than when the SOC is increased from the state where the SOC has not reached 100% to the target SOC 130%. Thus the time required to fill the gas tank with the gas can be shorter in the former case. Therefore, it is more preferable to supply the gas from the gas station to the gas tank while circulating the gas by the gas cooling unit between the gas tank and the gas station after the temperature of the gas in the gas tank rises to a predetermined temperature

The program can be stored and provided to a computer using any type of non-transitory computer readable media. Non-transitory computer readable media include any type of tangible storage media. Examples of non-transitory computer readable media include magnetic storage media (such as floppy disks, magnetic tapes, hard disk drives, etc.), optical magnetic storage media (e.g. magneto-optical disks), CD-ROM (compact disc read only memory), CD-R (compact disc recordable), CD-R/W (compact disc rewritable), and semiconductor memories (such as mask ROM, PROM (programmable ROM), EPROM (erasable PROM), flash ROM, RAM (random access memory), etc.). The program may be provided to a computer using any type of transitory computer readable media. Examples of transitory computer readable media include electric signals, optical signals, and electromagnetic waves. Transitory computer readable media can provide the program to a computer via a wired communication line (e.g. electric wires, and optical fibers) or a wireless communication line.

From the invention thus described, it will be obvious that the embodiments of the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims. 

What is claimed is:
 1. A gas filling system comprising: a gas tank; and a gas station configured to supply a gas to the gas tank, wherein the gas station comprises: a gas feed line configured to feed the gas from the gas station to the gas tank; a gas return line configured to return the gas in the gas tank to the gas station; a gas circulation pump configured to circulate the gas between the gas tank and the gas station through the gas feed line and the gas return line; and a gas cooling unit configured to cool the gas fed from the gas station to the gas tank through the gas feed line, and the gas is supplied from the gas station to the gas tank while the gas cooled by the gas cooling unit to a temperature lower than a heat resistant temperature of the gas tank is being circulated between the gas tank and the gas station.
 2. The gas filling system according to claim 1, wherein after a temperature of the gas in the gas tank has risen to a predetermined temperature, the gas is being supplied from the gas station to the gas tank while the gas is being circulated by the gas cooling unit between the gas tank and the gas station.
 3. The gas filling system according to claim 1, wherein the gas tank is mounted on a vehicle, and the vehicle comprises a gas feeding connection port for connecting the gas tank to the gas feed line and a gas returning connection port for connecting the gas tank to the gas return line, and shapes of connection parts of the gas feeding connection ports and the gas returning connection port differ from each other. 